There is a known interactive system including a projector that projects an image and a light emitting pen that is operated by a user on the projected image (see PTL 1, for example). The light emitting pen emits infrared light through the nib thereof, and the projector detects the infrared light emitted from the light emitting pen and recognizes what user's operation is. In a proposed interactive system of this type, the projector also includes a light emitting device that emits infrared light for synchronized communication between the projector and the light emitting pen. In this system, the light emitting pens emits light in response to the infrared light emitted from the projector.